feat(editor): Ctrl+Cut inserts a transparent band

README.md

@@ -37,6 +37,8 @@ resizable vector layers and preserves the monitor's native pixels on scaled disp
   mesh-gradient backdrops, and rendered drop shadows on standard backdrop cards.
 - Cut tool: drag across a band of the image to remove it and collapse the gap, with a
   live preview and dashed seam marker while dragging; annotations shift to follow.
+  Hold **Ctrl** (or **Ctrl+X**) to insert a transparent band instead; the toolbar
+  icon swaps to a split-plus while Ctrl is down.
 - Pin a finished capture as a bottom-right always-on-top layer surface, launched
   from the same `omasnap` executable and visible on every workspace.
 - Crash-resistant working documents under `/run/user/<UID>/omasnap/` (falling back to
@@ -361,7 +363,7 @@ without reaching for the pointer.
 | `R` | Rectangle; hover the shape button for rectangle, ellipse, and fill controls; `Alt`+wheel rounds corners |
 | `E` | Ellipse; shares the shape submenu and filled/hollow toggle |
 | `D` | Redact; press again to toggle randomized pixelation or solid redaction |
-| `X` | Cut out a band; drag to preview the crossed-out strip, then release to remove and collapse it |
+| `X` | Cut out a band; drag to preview the crossed-out strip, then release to remove and collapse it. **Ctrl** (with Cut armed, or **Ctrl+X**) inserts a band instead; the cut icon becomes a split-plus |
 | `T` | Text on a cream readability pill, with Neucha as the default. Click for a one-line label, or drag a box to give it room for several lines: Enter moves to the next line while there is room and commits on the last one; `Shift+Enter` always adds a line; `Esc` commits too but keeps the label selected, so `Backspace` removes it; clicking away keeps the text; press T again to toggle the pill |
 | `Shift+T` | Cycle the next or selected text through Neucha, JetBrains Mono, and Inter Display |
 | `O` | Recognize and copy all text in the current image |

docs/editing-model.md

@@ -42,9 +42,10 @@ Two operations *do* need to touch real pixels before export, and both are
 still fully undoable because of how they're kept in the log:
 
 - **Cut** (`Operation::Type::Cut`) removes a band of the image and shifts
-  everything after it. The working image (`capture_.source`) after a cut is
-  `composeCuts(pristineSource_, cuts_)` — recomputed from the untouched
-  original plus the list of cut ops every time the list changes
+  everything after it, or **inserts** a transparent band (`cut.insert`) and
+  shifts everything after the seam out. The working image (`capture_.source`)
+  after a cut is `composeCuts(pristineSource_, cuts_)` — recomputed from the
+  untouched original plus the list of cut ops every time the list changes
   (`CaptureEditor::refreshComposedCapture()`). Undo a cut and the composed
   image is rebuilt without it; `pristineSource_` was never modified.
 - **Redaction** exists to permanently destroy sensitive content, so it is

src/capture.cpp

@@ -1821,6 +1821,8 @@ QJsonObject operationToJson(const Operation &operation) {
     object.insert(QStringLiteral("sourceEnd"), operation.cut.sourceEnd);
     object.insert(QStringLiteral("logicalStart"), operation.cut.logicalStart);
     object.insert(QStringLiteral("logicalEnd"), operation.cut.logicalEnd);
+    if (operation.cut.insert)
+      object.insert(QStringLiteral("insert"), true);
     break;
   }
   return object;
@@ -1894,6 +1896,7 @@ bool operationFromJson(const QJsonObject &object, Operation &operation,
         object.value(QStringLiteral("logicalStart")).toInt();
     operation.cut.logicalEnd =
         object.value(QStringLiteral("logicalEnd")).toInt();
+    operation.cut.insert = object.value(QStringLiteral("insert")).toBool();
     return true;
   }
   error = QStringLiteral("Operation log has an unknown operation type");

src/cut.cpp

@@ -1,6 +1,5 @@
-/** @fileoverview Band cut-out engine: removes a horizontal or vertical band
- *  from an image and collapses the gap (Snagit-style "cut out", ported from
- *  omapic). */
+/** @fileoverview Band cut engine: removes a horizontal or vertical band and
+ *  collapses the gap, or inserts transparent space at the seam. */
 #include "cut.hpp"
 
 #include <QPainter>
@@ -44,27 +43,82 @@ QImage removeBand(const QImage &source, Qt::Orientation orientation,
   return out;
 }
 
+QImage insertBand(const QImage &source, Qt::Orientation orientation,
+                  int start, int end) {
+  if (source.isNull())
+    return source;
+  const int extent =
+      orientation == Qt::Horizontal ? source.height() : source.width();
+  start = std::clamp(start, 0, extent);
+  end = std::clamp(end, start, extent);
+  const int band = end - start;
+  if (band <= 0)
+    return source;
+  QImage image = source;
+  if (image.format() != QImage::Format_ARGB32 &&
+      image.format() != QImage::Format_ARGB32_Premultiplied)
+    image = image.convertToFormat(QImage::Format_ARGB32_Premultiplied);
+  if (orientation == Qt::Horizontal) {
+    const int height = image.height();
+    QImage out(image.width(), height + band, image.format());
+    out.setDevicePixelRatio(image.devicePixelRatio());
+    out.fill(Qt::transparent);
+    for (int y = 0; y < start; ++y)
+      std::memcpy(out.scanLine(y), image.constScanLine(y), image.bytesPerLine());
+    for (int y = start; y < height; ++y)
+      std::memcpy(out.scanLine(y + band), image.constScanLine(y),
+                  image.bytesPerLine());
+    return out;
+  }
+  const int width = image.width();
+  QImage out(width + band, image.height(), image.format());
+  out.setDevicePixelRatio(image.devicePixelRatio());
+  out.fill(Qt::transparent);
+  QPainter painter(&out);
+  painter.setCompositionMode(QPainter::CompositionMode_Source);
+  painter.drawImage(QPoint(0, 0), image, QRect(0, 0, start, image.height()));
+  painter.drawImage(QPoint(start + band, 0), image,
+                    QRect(start, 0, width - start, image.height()));
+  return out;
+}
+
+QImage applyCutOp(const QImage &source, const CutOp &cut) {
+  return cut.insert ? insertBand(source, cut.orientation, cut.sourceStart,
+                                 cut.sourceEnd)
+                    : removeBand(source, cut.orientation, cut.sourceStart,
+                                 cut.sourceEnd);
+}
+
 QImage composeCuts(const QImage &pristine, const QVector<CutOp> &cuts) {
   QImage image = pristine;
   for (const CutOp &cut : cuts)
-    image = removeBand(image, cut.orientation, cut.sourceStart, cut.sourceEnd);
+    image = applyCutOp(image, cut);
   return image;
 }
 
 QSize composedLogicalSize(QSize pristineLogical, const QVector<CutOp> &cuts) {
   for (const CutOp &cut : cuts) {
     const int band = cut.logicalEnd - cut.logicalStart;
+    if (band <= 0)
+      continue;
+    if (cut.insert) {
+      if (cut.orientation == Qt::Horizontal)
+        pristineLogical.setHeight(pristineLogical.height() + band);
+      else
+        pristineLogical.setWidth(pristineLogical.width() + band);
+      continue;
+    }
     if (cut.orientation == Qt::Horizontal) {
       const int extent = pristineLogical.height();
       // Mirror removeBand()'s no-op guard so this can never disagree with
       // what composeCuts() actually produces: an empty or full-extent band
       // leaves the image unchanged.
-      if (band <= 0 || band >= extent)
+      if (band >= extent)
         continue;
       pristineLogical.setHeight(std::max(1, extent - band));
     } else {
       const int extent = pristineLogical.width();
-      if (band <= 0 || band >= extent)
+      if (band >= extent)
         continue;
       pristineLogical.setWidth(std::max(1, extent - band));
     }
@@ -79,3 +133,9 @@ qreal shiftForCut(qreal value, qreal start, qreal end) {
     return value - (end - start);
   return start;
 }
+
+qreal shiftForInsert(qreal value, qreal start, qreal size) {
+  if (size <= 0.0 || value < start)
+    return value;
+  return value + size;
+}

src/cut.hpp

@@ -18,6 +18,7 @@ struct CutOp {
   int sourceEnd = 0;
   int logicalStart = 0;
   int logicalEnd = 0;
+  bool insert = false;
   bool operator==(const CutOp &) const = default;
 };
 
@@ -28,6 +29,14 @@ struct CutOp {
                                 Qt::Orientation orientation, int start,
                                 int end);
 
+/** Inserts a transparent band `[start, end)` and shifts the rest out. An
+ *  empty band is a no-op. */
+[[nodiscard]] QImage insertBand(const QImage &source,
+                                Qt::Orientation orientation, int start,
+                                int end);
+
+[[nodiscard]] QImage applyCutOp(const QImage &source, const CutOp &cut);
+
 /** Replays `cuts` in order over the pristine image. */
 [[nodiscard]] QImage composeCuts(const QImage &pristine,
                                  const QVector<CutOp> &cuts);
@@ -39,3 +48,7 @@ struct CutOp {
 /** Shifts one coordinate for a removed band [start, end): values past the
  *  band shift back by the band size, values inside clamp to the seam. */
 [[nodiscard]] qreal shiftForCut(qreal value, qreal start, qreal end);
+
+/** Shifts one coordinate for an inserted band of `size` at `start`: values
+ *  on or past the seam move out by `size`. */
+[[nodiscard]] qreal shiftForInsert(qreal value, qreal start, qreal size);